Effects of season on the agar content and chemical characteristics of Gracilaria cornea from Yucatan, Mexico

Chemical characteristics and gelling properties of native and alkali treated agar were studied from Gracilaria cornea growing at the Yucatan coast. Plants were collected during the seasons of 1995 to 1996 (dry, rainy and cold). Agar yield, gel strength, gelling and melting temperatures, sulphate and 3,6 anhydro-galactose content were determined. Percent dry weight, soluble carbohydrate and carbon content were measured on algal tissue. There was a clear seasonality in the yield and gel strength in native and alkali treated agars. In general, the yield was higher for the native agar extracts. Agar yield increased from the dry to the rainy season and lowest yield was found in the cold season. The yield of alkali treated agar had a maximum during the cold season (31.6%) but was lowest during the rainy season (21.4%). Gel strength (1.5% concentration) increased when alkali treatment was carried out and was highest during the dry season (1653 g cm(-2)). Sulphate content ranged between 4.8-5.47% and decreased significatively when the seaweed was alkali treated (1.18-1.56%). Alkali modification increased the 3,6 anhydro-galactose content from 31.6-32.5% to 38.3-42.9% depending on the season. Maximum gelling (41.8 +/- 0.5 degrees C) and melting (89 +/- 0.4 degrees C) temperatures of treated agar and highest gel strength were found for plants harvested during the dry season. Agar from G. cornea is of sufficient quality and yield to be considered an excellent potential source for industrial use.